'\" te
.\"  Copyright (c) 2007, Sun Microsystems, Inc., All Rights Reserved
.\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License").  You may not use this file except in compliance with the License.
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.TH LDI_EV_REGISTER_CALLBACKS 9F "Oct 24, 2012"
.SH NAME
ldi_ev_register_callbacks \- add a notify and/or finalize callback
.SH SYNOPSIS
.nf
#include <sys/sunldi.h>

\fBint\fR \fBldi_ev_register_callbacks\fR(\fIldi_handle_t lh\fR,
      \fIldi_ev_cookie_t *cookie\fR, \fIldi_ev_callback_t *callb\fR,
      \fBvoid\fR \fI*arg\fR, \fIldi_callback_id_t *id\fR);
.fi

.SH INTERFACE LEVEL
illumos DDI specific (illumos DDI)
.SH PARAMETERS
.ne 2
.na
\fB\fIldi_handle_t lh\fR\fR
.ad
.sp .6
.RS 4n
A layered handle representing the device for which the event notification was
requested.
.RE

.sp
.ne 2
.na
\fB\fIldi_ev_cookie_t *cookie\fR\fR
.ad
.sp .6
.RS 4n
An opaque event cookie for the event type returned by a previous call to
\fBldi_ev_get_cookie\fR(9F).
.RE

.sp
.ne 2
.na
\fB\fIldi_ev_callback_t *callb\fR\fR
.ad
.sp .6
.RS 4n
A data structure which currently has the following members:
.sp
.in +2
.nf
struct ldi_ev_callback {
        uint_t  cb_vers;
        int     (*cb_notify)(ldi_handle_t,
                             ldi_ev_cookie_t cookie,
                             void *arg, void *ev_data);
        void    (*cb_finalize)(ldi_handle_t,
                               ldi_ev_cookie_t cookie,
                               int ldi_result,
                               void *arg,
                               void *ev_data);
 } ldi_ev_callback_t;
.fi
.in -2

where
.sp
.ne 2
.na
\fB\fBcb_vers\fR\fR
.ad
.RS 11n
Version of callback vector. Must be set to \fBLDI_EV_CB_VERS\fR by the caller.
.sp
The arguments passed into the callbacks when they are invoked, include:
.sp
.ne 2
.na
\fB\fBint ldi_result\fR\fR
.ad
.sp .6
.RS 4n
The actual result of the state change operation/event passed to finalize
callback: \fBLDI_EV_SUCCESS\fR: The state change succeeded
\fBLDI_EV_FAILURE\fR: The state change failed.
.RE

.sp
.ne 2
.na
\fB\fBvoid *ev_data\fR\fR
.ad
.sp .6
.RS 4n
Event specific data.
.RE

.RE

.RE

.sp
.ne 2
.na
\fB\fBvoid\fR *\fIarg\fR\fR
.ad
.sp .6
.RS 4n
A pointer to opaque caller private data.
.RE

.sp
.ne 2
.na
\fB\fIldi_callback_id_t *id\fR\fR
.ad
.sp .6
.RS 4n
Unique system wide registration id returned by ldi_ev_register_callbacks(9F)
upon successful registration.
.RE

.SH DESCRIPTION
The \fBldi_ev_register_callbacks()\fR interface allows layered drivers to
register notify and finalize callbacks for certain events. These events are
listed in the \fBldi_ev_get_cookie\fR(9F) man page. The notify callback is
invoked only for events that can be blocked, just before the event occurs. The
notify event is not called for events serviced by the \fBNDI\fR event  service
framework since such events are by definition asynchronous. Only  the finalize
callback is invoked for such events. Layered drivers that have registered
notify callbacks for that event have the opportunity of blocking such events.
The finalize callback is invoked once the final disposition of the state of a
device (specifically a device minor node) is known. The callback is invoked
with this result, either \fBLDI_EV_SUCCESS\fR (state change succeeded) or
\fBLDI_EV_FAILURE\fR (state change failed). This allows layered driver
consumers to finalize any changes they made in response to a previous "notify"
callback.
.sp
.LP
For example, a layered driver's notify callback may be invoked in response to a
\fBLDI_EV_OFFLINE\fR event. The layered driver may reconfigure itself to stop
using the device and permit the change to go forward. Once that happens, the
\fBI/O\fR framework attempts to actually take the device offline. This offline
attempt can have two possible outcomes: success or failure. In the former case,
the finalize callback is invoked with the \fIldi_result\fR argument set to
\fBLDI_EV_SUCCESS\fR and the layered driver knows that the device has been
taken offline. In the latter case, finalize is invoked with the
\fIldi_result\fR set to \fBLDI_EV_FAILURE\fR and the layered driver knows that
the state change failed. In this case, it may choose to reconfigure itself to
start using the device again.
.sp
.LP
Finalize callbacks can be registered for all events including events that
cannot be blocked.
.sp
.LP
A layered driver can also propagate these events up the software stack by using
interfaces offered by the \fBLDI\fR event framework. The layered driver may use
\fBldi_ev_notify()\fR to propagate notify events occurring on minors it imports
onto minors it exports. Similarly, it may use \fBldi_ev_finalize()\fR to
propagate finalize events. Both \fBldi_ev_notify()\fR and
\fBldi_ev_finalize()\fR propagate events to device contracts as well as LDI
callbacks  registered against the exported minor nodes.
.sp
.LP
The \fBLDI\fR event framework has the following guarantees and requirements
with respect to these callbacks:
.RS +4
.TP
1.
The \fBnotify()\fR callback is invoked before an event (represented by the
event cookie) occurs on a device (represented by the layered driver handle) and
is invoked only for events that can be blocked. If the callback returns
\fBLDI_EV_FAILURE\fR, the event is blocked. If the callback returns
\fBLDI_EV_SUCCESS\fR, the event is allowed to proceed. If any other value is
returned, it is an error. An error message is logged and the event is blocked.
An example of an event that can be blocked and for which notify callbacks may
be invoked is the offline event \fBLDI_EV_OFFLINE\fR.
.RE
.RS +4
.TP
2.
The finalize callback is invoked for all events (including events that
cannot be blocked) after the event has occurred. It is invoked with either
\fBLDI_EV_SUCCESS\fR indicating that the event successfully happened or
\fBLDI_EV_FAILURE\fR indicating that the event did not occur. The finalize
callback returns no values. Good examples of events that cannot be blocked are
the degrade event (\fBLDI_EV_DEGRADE\fR) and events serviced by the \fBNDI\fR
event service framework.
.RE
.RS +4
.TP
3.
Layered drivers may register one or both of these callbacks (that is, only
for a notify event or only for a finalize event or for both) against any
\fBLDI\fR handle that they may possess. If a finalize or notify event is not
being registered, the corresponding pointer in the \fIldi_ev_callback_t\fR
structure must be set to \fBNULL\fR. It is an error to attempt a registration
with both callbacks set to \fBNULL\fR.
.RE
.RS +4
.TP
4.
A notify and/or finalize callback is invoked only if the corresponding
\fBLDI\fR handle is open. If an \fBLDI\fR handle against which the callbacks
are registered is closed, the corresponding finalize and notify callbacks is
not invoked as it is assumed that the layered driver is no longer interested in
the device. See number 5 below for the exception to this rule.
.RE
.RS +4
.TP
5.
A layered driver that closes it's \fBLDI\fR handle in it's notify routine
receives the corresponding finalize callback after the event has occurred.
Because the \fBLDI\fR handle has been closed, the finalize callback is invoked
with a \fBNULL\fR \fBLDI\fR handle. It is the responsibility of the layered
driver to maintain state in it's private "\fIarg\fR" parameter so that it can
reopen the device (if desired) in it's finalize callback.
.sp
One example where this may happen is with the \fBLDI_EV_OFFLINE\fR event. A
layered driver's notify callback may be invoked for an offline event. The
layered driver may choose to allow this event to proceed. In that case, since
it has a layered open of the device, it must close the \fBLDI\fR handle so that
the offline event can succeed (an offline of a device does not succeed if there
is any open of the device, layered or otherwise). Since the layered driver has
closed the \fBLDI\fR handle in the notify routine, it's finalize callback (if
any) is invoked with a \fBNULL\fR \fBLDI\fR handle. It is the responsibility of
the layered driver to maintain state (such as the device path or \fBdevid\fR)
in it's private "\fIarg\fR" parameter, so that in the finalize routine, it can
do a layered open of the device if the device offline failed.
.sp
This is the only exception where the finalize callback is invoked if the
\fBLDI\fR handle has been closed. In all other cases if the \fBLDI\fR handle
has been closed, no corresponding callbacks is invoked.
.RE
.RS +4
.TP
6.
In order for the offline event to succeed (\fBLDI_EV_OFFLINE\fR), it is
imperative that there be no opens (including \fBLDI\fR handles) to the device.
If a layered driver's notify callback is invoked for an offline event and the
driver intends to allow the offline to proceed, the driver must close the
corresponding \fBLDI\fR handle.
.RE
.RS +4
.TP
7.
The notify and finalize callbacks are not automatically unregistered even if
the corresponding \fBLDI\fR handle has been closed. It is the responsibility of
the layered driver to unregister these callbacks when they are not required. It
may do so using the \fBldi_ev_remove_callbacks\fR(9F) interface. The \fBLDI\fR
framework may panic if the entity registering the callback (such as a
\fBdip\fR, \fBdev_t\fR or \fBmodule\fR) no longer exists on the system and the
corresponding callbacks have not been unregistered.
.RE
.RS +4
.TP
8.
The \fBLDI\fR event framework guarantees that if a layered driver receives a
notify event, it also receives a finalize event except if the layered consumer
itself blocked the event (that is, it returned \fBLDI_EV_FAILURE\fR from it's
notify callback. In this case, the layered driver knows that the event has been
blocked and therefore does not need the finalize callback.
.RE
.RS +4
.TP
9.
If a layered driver propagates notify events on minors it imports to minors
it exports, it must first propagate these events up the software stack via
\fBldi_eve_notify()\fR in it's notify callback. It must do so before attempting
to check if it blocks the event. This is required, because a layered driver
cannot release the device if consumers up the stack are still using the device.
If \fBldi_ev_notify()\fR returns \fBLDI_EV_FAILURE\fR, the callback must
immediately return \fBLDI_EV_FAILURE\fR from it's notify callback. If
\fBldi_ev_notify()\fR  returns \fBLDI_EV_SUCCESS\fR, then the state change is
permissible as far as consumers higher up in the software stack are concerned.
The layered driver must then determine if it can permit the state change. If
the state change is to be allowed, the layered driver must return
\fBLDI_EV_SUCCESS\fR. If the layered driver determines that the state change
should not be permitted, it must invoke \fBldi_ev_finalize()\fR  on minors it
exports with a result of \fBLDI_EV_FAILURE\fR (to inform consumers up the
stack) and then return \fBLDI_EV_FAILURE\fR from it's notify callback.
.RE
.RS +4
.TP
10.
The \fBLDI\fR event framework generates finalize events at the earliest
point where a failure is detected. If the failure is detected in the framework
(such as in \fBldi_ev_notify()\fR) the framework generates the finalize events.
In the event that a failure is first detected in a layered driver (that is, in
the notify callback of a layered driver) the layered driver must use
\fBldi_ev_finalize()\fR  to send finalize events up the software stack . See
the examples for code snippets describing this scenario.
.RE
.RS +4
.TP
11.
The finalize callback must first reconfigure itself before attempting to
propagate the event up the software stack via \fBldi_ev_finalize\fR(9F). This
is so that the minors it exports are available and ready for use before the
finalize event is propagated up the software stack.
.RE
.RS +4
.TP
12.
It may so happen that the event propagated up the software stack is not the
same as the event for which a layered driver's notify/finalize callback is
invoked. For example, a layered driver's callback(s) may be invoked for an
offline event, but the driver may choose to only propagate the degraded event
to its consumers (since it may have a mirror/copy of the data on the device.)
In that case, the layered driver must generate a different event cookie (that
is, one corresponding to the degraded event via \fBldi_ev_get_cookie\fR(9F))
and use that cookie in its propagation calls (that is, \fBldi_ev_notify\fR(9F)
and \fBldi_ev_finalize\fR(9F)).
.RE
.sp
.LP
Once the registration of the callback(s) is successful, an opaque
\fIldi_callback_id_t\fR structure is returned which may be used to
unregister the callback(s) later.
.SH RETURN VALUES
The return values for this function are:
.sp
.ne 2
.na
\fB\fBLDI_EV_SUCCESS\fR\fR
.ad
.sp .6
.RS 4n
Callback(s) added successfully.
.RE

.sp
.ne 2
.na
\fB\fBLDI_EV_FAILURE\fR\fR
.ad
.sp .6
.RS 4n
Failed to add callback(s).
.RE

.SH CONTEXT
This function can be called from user and kernel contexts only.
.SH EXAMPLES
\fBExample 1 \fRRegistration and Callbacks for the OFFLINE Event
.sp
.LP
The following example shows how the \fBldi_ev_register_callbacks()\fR function
performs a registration and callback for the offline event:

.sp
.in +2
.nf
static int
event_register(void)
{
        ldi_handle_t lh;
        ldi_ev_callback_t callb;
        ldi_ev_cookie_t off_cookie;

        if (ldi_ev_get_cookie(lh, LDI_EV_OFFLINE, &off_cookie)
            == LDI_EV_FAILURE)
                goto fail;


        callb.cb_vers = LDI_EV_CB_VERS;
        callb.cb_notify = off_notify;
        callb.cb_finalize = off_finalize;

        if (ldi_ev_register_callbacks(lh, off_cookie, &callb, arg, &id)
            != LDI_EV_SUCCESS)
                goto fail;
}

static void
event_unregister(ldi_callback_id_t id)
{
        ldi_ev_remove_callbacks(id);
}

static int
off_notify(ldi_handle_t lh, ldi_ev_cookie_t off_cookie, void *arg,
    void *ev_data)
{

        ASSERT(strcmp(ldi_ev_get_type(off_cookie), LDI_EV_OFFLINE) == 0);

        /* Map imported minors to exported minor */
        widget_map(lh, &minor, &spec_type);

        /*
         * Call ldi_ev_notify() to propagate events to our consumers.
         * This *must* happen before we check if offline should be blocked
         */
        if (ldi_ev_notify(dip, minor, spec_type, off_cookie, ev_data)
            != LDI_EV_SUCCESS)
                return (LDI_EV_FAILURE);

        /*
         * Next, check if we can allow the offline
         */
        if (widget_check(lh) == WIDGET_SUCCESS) {
                widget_save_path(arg, lh);
                widget_reconfigure(lh, RELEASE);
                ldi_close(lh);
                return (LDI_EV_SUCCESS)
        }

        /*
         * We cannot permit the offline. The first layer that detects
         * failure i.e. us, must generate finalize events for our
           consumers
         */
        ldi_ev_finalize(dip, minor, spec_type, LDI_EV_FAILURE, off_cookie,
            ev_data);

        return (LDI_EV_FAILURE);
}

/*
/*
 * The finalize callback will only be called if we returned LDI_EV_SUCCESS
 * in our notify callback. ldi_result passed in may be SUCCESS or FAILURE
 */
static void
off_finalize(ldi_handle_t NULL_lh, ldi_ev_cookie_t off_cookie,
    int ldi_result, void *arg, void *ev_data)
{
        ldi_handle_t lh;

        ASSERT(strcmp(ldi_ev_get_type(off_cookie), LDI_EV_OFFLINE) == 0);

        path = widget_get_path(arg);

        widget_map_by_path(path, &minor, &spec_type);

        if (ldi_result == LDI_EV_SUCCESS) {
                ldi_ev_finalize(dip, minor, spec_type, LDI_EV_SUCCESS,
                    off_cookie, ev_data);
                return;
        }

        /* The offline failed. Reopen the device */
        ldi_open_by_name(path, &lh);
        widget_reconfigure(lh, REACQUIRE);

        ldi_ev_finalize(dip, minor, spec_type, LDI_EV_FAILURE, off_cookie,
            ev_data);
}
.fi
.in -2

.LP
\fBExample 2 \fRRegistration and Callbacks for the DEGRADE Event
.sp
.LP
The following example shows how the \fBldi_ev_register_callbacks()\fR function
performs a registration and callback for the degrade event:

.sp
.in +2
.nf
static int
event_register(void)
{
        ldi_handle_t lh;
        ldi_ev_callback_t callb;
        ldi_ev_cookie_t dgrd_cookie;

        if (ldi_ev_get_cookie(lh, LDI_EV_DEGRADE, &dgrd_cookie)
            == LDI_EV_FAILURE)
                goto fail;

        /* no notify callbacks allowed for degrade events */
        callb.cb_vers = LDI_EV_CB_VERS;
        callb.cb_notify = NULL; /* NULL, notify cannot be used for
                                   DEGRADE */
        callb.cb_finalize = dgrd_finalize;

        if (ldi_ev_register_callbacks(lh, dgrd_cookie, &callb, arg, &id)
            != LDI_EV_SUCCESS)
                goto fail;
}

static void
event_unregister(ldi_callback_id_t id)
{
        ldi_ev_remove_callbacks(id);
}

/*
 * For degrade events. ldi_result will always be LDI_EV_SUCCESS
 */
static void
dgrd_finalize(ldi_handle_t lh, ldi_ev_cookie_t off_cookie,
    int ldi_result, void *arg, void *ev_data)
{
        ASSERT(ldi_result == LDI_EV_SUCCESS);
        ASSERT(strcmp(ldi_ev_get_type(off_cookie), LDI_EV_DEGRADE) == 0);

        widget_map(lh, &minor, &spec_type);

        widget_reconfigure(lh, RELEASE);

        ldi_ev_finalize(dip, minor, spec_type, LDI_EV_SUCCESS, d
            grd_cookie, ev_data);
}
.fi
.in -2

.SH SEE ALSO
.BR ldi_ev_finalize (9F),
.BR ldi_ev_get_cookie (9F),
.BR ldi_ev_notify (9F),
.BR ldi_ev_remove_callbacks (9F)
